Manufacture of tubing



Sept. 9, 1941. c. A. NICHOLS ETAL MANUFACTURE OF TUBING Filed Nov. 9, 1938 2 Sheets-Sheet l l/ I L Sept. 9, 1941.

C; A. NICHOLS ET AL MANUFACTURE OF TUBING Filed Nov. 9, 1938 2 Sheets-Sheet 2 9 o z m Patented Sept. 9, 1941 MANUFACTURE OF TUBING Charles A. Nichols and Raymond H. Bish, Anderson, Ind., assignors to GeneralMotors Corporaton, Detroit, Mich., a eorporation of Delaware Application November 9, 1938, Serial No. %9,655

3 Claims.

This invention relates to the manufacture of seamed tubing including seamed multi-ply tubing, the plies and seams of which are bonded together by an intermediate scaling metal such as copper.

In welding with molten copper it is necessary that the temperature of that portion of the tubing immersed in the molten copper be above the melting point of copper. Preferably the temperature of the bath .of copper is approximately 2100 F. Heretofore the application of molten copper to seamed tubing has been performed in an electric furnace having resistance heating elements from which heat is radiated to the bath of copper to keep the same in molten condition. The furnace includes also a preheated zone in which the temperature of the tubing is raised to the required temperature for copper welding by means of heat radiating from resistance heating elements. The tubing being heated as well as the bath of copper is protected by a non-oxidizing or reducing atmosphere in order to prevent oxidation of the tubing or of the copper in the bath. As the rate of production of copper welded tubing is largely dependent upon the rate of transfer of heat from the resistance elements to the furnace atmosphere and to the tubing passing through it and to the parts containing the bath of copper, it is evident that a furnace of relatively large size is required. For example, we have found that a furnace approximately ft. long is required for copper welding seam steel tubing at a rate of 25 ft. per minute.

The chief aim and object of the present invention is to provide an improved method and 4 apparatus by which seamed steel tubing may be copper welded at a much higher speed of production and with much more effective utilization of electric current for heating the tubing and the bath of copper. These aims and objects are accomplished by providing a relativeiy small electric furnace enclosing the vessel for containing the bath of copper, said furnace being heated by resistance elements of a highly concentrated nature commercially known as glow bars." Glow bars are rods of special resistance material so constructed as to provide for the application of intense heat within a small space. We have found the glew bar method of heating the copper bath to be very effective. In. order to provide for heating the tubing without unduly extractlng heat from the copper bath we prefer heating the tubing by separate means to bring the tubing nearly to the proper copper welding temperature. This heating means is preferably provided by passing an electric current directly through the tubing while it is moving from the tubeforming mill to the copper bath. Since the tubing moves through the copper bath, the bath itself can be made one terminal or electrode of the circuit through the tubing. A pair of metal rolls applying pressure to the tubing while it is still relatively cold provides the other electrode or terminal for the tube heating circuit. While the tubing is being heated before passing into the bath it is protected by a surrounding atmosphere of non-cxidizing or reducing gas which passes through a pipe surrounding the tubing leading to the interior of the furnace.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the invention is clearly shown.

In the drawings:

Figs. 1 and 2 taken together constitute a plan view, partly fragmentary, of apparatus embodying the present invention.

Figs. 3 and 4 taken together constitute a side view thereof partly in section.

Fig. 5 is a fragmentary longitudinal sectional view of the furnace drawn to a larger scale than Fig. 3.

Fig. 6 is a sectional view on the line 5-5 of Fig. 5.

Referrng to the drawings, the work or tubing is indicated by the letter T. The tubing is formed from strip stock in any suitable manner and passes between pressure rolls 20 and 2I made preferably of copper and geared together and driven by an electric motor 22 in such direction as to feed the tubing from left toward right as viewed in the drawings.

The tubing Tfirst moves through a chamber 23 to which a suitable non-oxldizing or reducng gas is supplied to a pipe 24. Pipe 23 leads to the interior chamber 25 of furnace 26 to supply the same non-oxidizing gas, the gas being under such pressure as to exclude air from the furnace open ing 2'l on the right hand side thereof. The bottom wall 28 of the furnace chamber supports a track 29 upon which rests a small vessel or tank 30 of highly refractory metal for containing a bath of'copper, the normal level of which is indicated at 3| in Figs. 5 and 6. The vessel 30 is provided with a flared opening 32 through which the tubing T p'asses on entering the chamber within the vessel. The tubing'passes through `an fire clay or the like. through a gas wiper block 35 having a stepped bore comprising steps 35, 31, and 38 which are cylindrical and a portion 39 which is conical or flared. Bore 35 flts fairly close around the tubing T, but not so closely as to interfere with its movement. Bores 31 and 38 are increasingly larger. The bore 31 communicates with an annular groove !u closed by band Al having a hole 42 connected by a pipe 43 with a wiper gas heater stove 44 which comprises four horizontal pipes 45 connected by vertical pipes 45. Into the lower-most one of the pipes 45 a reducing gas is admitted under pressure through the' pipe fll shown in Fig. 1. This gas is forced through the stove 44', through the annular groove Noi wiper block 35 and out through the annular passages between the tubing T and the stepped heres 38, 31, and 38. As the bar 36 fits the tubing T i'airly closely most of this wiper gas passes out through the bores 31, 38 and 39 for the purpose of removing excess copper from the tubing. The baiile 34 directs the blast of wiper gas and globules of molten copper upwardly along the baiile 35.

In order to raise the level 3! of thecopper bath above the tubing T in order to submerge the tubing there is provided a plunger block 56 of reractory material supported by a bracket attached to a pipe'52 which extends through the top wall of the' furnace, there being a guide pipe 53 surrounding pipe 52. Above the top oi the urnace the pipe 52 is provided with collars 54 and 55 which ;together with the pipe provide' a groove for receiving studs 55 carried by bifurcated end 51 of a lever 58 pivoted at 59 upon a bracket 69 supported by the furnace. When the pipe 52 is held upwardly as shown in the drawings the level 3! and the copper will be below the tubing T. If the level 58 is moved clockwise as viewed in Fig, 3, pipe 53 will be lowered to cause the ;block 5!) to plunge into the bath of copper to displace the same to raise its level above the tubing T. Obviously this is done after the tubing has started moving through the urnace from left toward right. As the tubing moves through the side walis of the vessel 38 practically no copper escapes from the opening in these side walis because any copper which starts to flow out the opening :32 '(see Fig. 5) is dragged toward. the right by the moving tubing T. Any copper which tries to escape through the bores39, 38 and 3? is blown toward the left by the wiper gas issuing rrom the wiper block 35.

Bracket SI which supports the displacement block se is provided with a baille si which, when the block 50 is in lower-most position, is in close proximity to the bame 35. Thus the battles si and 34 cooperate to guide globules of gas biown by the wiper gas jet from the tubing back into the copper bath while the wiper gas may escape into the furnace chamber. obviousiy the gas in the furnace chanber willbe of such pressure as to exclude air from entering either of the pipes 52 or 53 as well as through the furnace opening 27. I

The copper bath receives its heat from glow bars 'm which are so constructed of special resistance material as to be capabie of carrying a large current and deveioping an 'intense beat which is radiated to the bath of copper to meit the same, the copper to be melted being introduced through the pipe 52 and to replenish the bath. Glow bars '16 are connected with electrodes ll and 12 shown diagrammatically in Fi 1 leading to a suitable'source of current.

Since we have found that there iS e limit to the rate of transfer of heat by radiation to a bath of copper, we have found it advantageous not to transmit from the bath to the tubing all of that heat which is necessary to bring the tubing up to the proper welding temperature. Therefore we provide means other than the copper bath itself for suppiyingto the tubing a part of the heat required to raise its temperature to welding temperature. We locate the rreme.. work se which supports the ;feed rolls 20 (preferably of copper) upon a nonconducting support Bi which insulates the frame BB from the supporting bracket 82. Frame 80 is connected with a wire 83 leading to a suitable current source, the

'other terminal of which is-comected by wire 84 with the metal rail 29 which supports the metal vessel 3% which contains the bath of copper. In this way that portion of the tubing T between the rolls 20 and ?i and the bath of copper in the vessei 36 carries an elec'tric current of such electrical dimensions as to heat the tubing T substantiaily. Preferably we preheat the tubing to about 1900 F. 'We are not required to be very accurate about this because the completion of the elevation of the temperature of the tubing is performed .by the copper bath itself so the tubing will not be rendered hotter than necessary. Thus current is conserved without requiring any temperature regulating apparatus of a reflned nature. The temperature of the furnace itself may be regulated automaticallyby a regulator not shown Operating in conjunction with a pyrometer indicated diagrammatically at 80 in Fig. 6.

So effective is our method and apparatu's for heating the tubing and copper :bath that we are able to materially speed up the rate of travel of the tubing T through the furnace. We can now copper-weld A" seem tubing at the rate of 50 ft. per minute, and might go still higher ii' we i employ tube-forming apparatus which will stand .in chamber m water, red from a pipe ill,

trickles upon the tubing and shelf il? and gravitates to the bottom of the vessel Hi! and out through a drain 3.

Finally, the tubing T passes between pressure pull-out rolls ii@ and iii which are geared together and are driven by an electric motor |22 in such direction as to cause the tubing to move from left toward right in the drawings. The

prill-out' rolls !28 and m cooperate with the eletric current carrying rolls 28 and 2! to propel the tubing through the furnace. The tube forming mili (not shown) also includes iorming rolls which cooperate with these rolls to move the tubing. In order that the force appiied by roils 25 and ?i for ieeding the tubing will be coordinated with other feed roils, thermotor 22 drives rolls 20 and ?i through a properly adjusted friction-slip-clu'tch 22a. Likewise motor |22 drives pull-out rolls ii and m through a frictionslip-cluth !2211. As steel tubing at high temperature in the presence of molten copper is hot-short and therefore relatively weak, the

clutch !22a is adjusted so that the traction effected by the pull-out rolls !20 and 2! will not be so great as to cause disruption of the tubing.

Legs or brackets !24 and !25 support shelves !26 and !21 which in turn support the vessel and the pull-out rolls !20 and !2! These legs !24 and !25 as well as the legs !04 and !05 supporting the water jacket !0! can be provided with casters or the like, so as to be easily moved along the floor. By moving the legs !04, !05, !24 and !25 toward the right from the position shown in the drawings, all of the apparatus supported by these legs will move to the right, carrying with it the lead-out pipe !00, leaving the wiper block 35 and wiper gas preheating stove 44 assembled therewith. Quite obvlously certain bricks may be removed from the opening 2'! of the furnace to permit withdrawal of these parts. The vessel 30 may be separately withdrawn along the track 29; or, if preferred, the lead-out pipe !00, wiper block 35, stove 44, and tray 30 may be made up as one assembly so as to slide along the track 29 when the apparatus supported by the legs !04, !05, !24 and !25 is moved toward the right.

Copper to replenish the bath in the tray 30 is provided by feeding a wire unreeled from a supply reel (not shown) and fed by a pair of geared feed rolls !30 and !3! operated by an electric motor !32 (see Fig. 1). This wiper passes upwardly along the side of the furnace and is guided over the top of the furnace and then down through the pipe 52. When the lower end of the copper wire touches the copper bath or any part heated above the melting point of copper, the copper wire will melt to supply what is needed to replenish the bath. The speed of feed of the copper wire can be regulated to-suit the conditions.

While the embodinent of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

Vfhat is claimed is as follows:

l. The method of welding seamed tubing while the tubing is continuously moving longitudinally which consists in maintaining a bath of molten welding metal at the proper temperature for welding the tubing, in preheating the moving tubing to a temperature below the welding temperature, immediately passing the preheated moving tubing through the bath, the bath being maintained in such quantity as to raise the temperature of the tubing to the welding temperature while the tubing passes through the bath.

2. The method of welding seamed tubing while the tubing is continuously moving longitudinally which consists in maintaining a bath of molten welding metal at the proper temperature for welding the tubing, in passing an electric current through a portion of the moving tubing extending from the bath to a point outside the bath to preheat the tubing to a temperature below the welding temperature, and in completing the heating of the moving tubing in the bath, the bath being maintained in such quantity as to raise the temperature of the tubing to the welding temperature while the tubing passes through the bath.

3. The method of welding seamed tubing while the tubing is continuously moving iongitudinally which consists in maintaining a bath of molten welding metal at the proper temperature for welding the tubing, in passing an electric current through the bath and a portion of the moving tubing extending from the bath to a. point outside the bath to preheat the tubing to a temperature below the welding temperature, and in completing the heating of the moving tubing in the bath, the bath being maintained in such quantityas to raise the temperature of the tubing to the welding temperature while the tubing passes through the bath.

- CHARLES A. NICHOLS.

RAYMOND H. BISH. 

